Investigations of the effects of modification of the riboflavin- binding protein on its role in vitamin transport to the egg are being continued. Effect of desialylation, oxidation of two non-reducing terminal galactose units, total removal of the major glycopeptide, removal of the phosphates, removal of the light chain on RBP retention in the blood, and efficacy of transfer of riboflavin to the yolk of rdrd laying hens will be observed. The above derivatives retain their vitamin-binding capacity and most of the immunodeterminants. Attempts to recover pro-RBP from RdRd hens and the altered pro-RBP from rdrd hens using a combination of ion exchange column chromatography, salt precipitation, and affinity chromatography have yielded small quantities of purified protein. Sufficient samples will be isolated to permit comparison of chemical properties with those of RBP (Peptide map, CHO and phosphorus content, molecular weight by equilibrium sedimentation methods). Further attempts to convert pro-RBP into an active form with controlled trypsin digests have been unsuccessful. The best results gave only 1 to 2 percent of the theoretical vitamin binding. Other proteolytic enzymes will be examined. Fractions of extracts of liver will be surveyed for the specific enzyme involved in the conversion of pro-RBP to RBP.